US20070285099A1 - Electrochemical Sensor - Google Patents
Electrochemical Sensor Download PDFInfo
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- US20070285099A1 US20070285099A1 US11/660,255 US66025505A US2007285099A1 US 20070285099 A1 US20070285099 A1 US 20070285099A1 US 66025505 A US66025505 A US 66025505A US 2007285099 A1 US2007285099 A1 US 2007285099A1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/416—Systems
- G01N27/48—Systems using polarography, i.e. measuring changes in current under a slowly-varying voltage
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- General Health & Medical Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
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- Secondary Cells (AREA)
- Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)
- Investigating Or Analysing Biological Materials (AREA)
- Electric Double-Layer Capacitors Or The Like (AREA)
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Abstract
Description
- The present invention relates to electrochemical sensors and electrochemical sensing methods.
- In an electrochemical biosensor, a working electrode is used with a counter electrode and a reference electrode, though the latter two may be combined as a pseudo-reference electrode. In the text below the term reference electrode should be construed as indicating pseudo-reference electrodes, unless the context otherwise requires. To make a measurement, a potential difference is applied between the working and reference electrode and the resulting current is measured over a range of voltages. The analyte concentration and analyte species present in a fluid can be derived from current measurements at specific potential differences. Complementary information can be derived from the measured voltammetric peak position (and/or mid point position) and voltammetric peak separation. An electrode that can be used in such biosensors is described in WO 03/056319 (which document is hereby incorporated in its entirety by reference).
- It has been discovered that measurements made on such a sensor can suffer from errors, particularly if rapid measurements are to be made on a portable device.
- Accordingly, the present invention provides an electrochemical sensing method comprising:
- applying a time-varying potential between working and reference electrodes in electrical contact with a target solution, said time varying potential having a ramp-up period, during which the potential difference increases from substantially zero to a first predetermined potential, and a plateau period during which said potential difference is maintained substantially constant at said first predetermined potential; and
- sampling the current flowing between said working and reference electrodes during said plateau period.
- The present inventors have determined that some errors in measurement derive from applying a step potential to the electrodes. The step rise in potential produces a current spike followed by a decay due in part to the capacitance of the electrodes—the form of the decay is also dependent on the concentration of the target solution and hence cannot be predicted—and the difficulties in sinking a high transient current in a portable device. Thus measurements are taken in a non-steady state and errors result.
- Preferably, the rate of potential change in the ramp-up period is less than or equal to about 250Vs−1, preferably less than about 150Vs−1 and most preferably in the range of from about 5 to 75Vs−1. Such a rate reduces the current peak caused by the potential increase so that measurements taken in the plateau period are substantially error-free.
- The time-varying potential may further comprise a second ramp-up period during which the potential difference increases from substantially zero to a second predetermined potential, and a second plateau period during which said potential difference is maintained substantially constant at said second predetermined potential; and the method further comprising sampling said current during said second plateau period.
- Repeating the ramp-up and measurements provides additional data points to improve averaging. In a particular embodiment the second predetermined potential is of the opposite polarity to the first predetermined potential and has a different magnitude, but in other embodiments the first and second predetermined potentials may have the same polarity.
- In a preferred embodiment of the invention, the potential difference in the ramp-up period(s) substantially follows a part of a sinusoidal function, in particular a half of a period. Such a waveform minimises current transients and is also relatively simple to generate in real time.
- The present invention is further described below with reference to an exemplary embodiment and the accompanying drawings, in which:
-
FIG. 1 is a schematic diagram of a portable electrochemical sensor device incorporating the invention; -
FIG. 2 is a graph of potential vs. time of a waveform applied to electrodes in an embodiment of the invention; and -
FIG. 3 is schematic of a basic potentiostat. - The sensor device comprises an
electronics unit 10 to which is connected anelectrode unit 20, which may be disposable. Theelectrode unit 20 has a plurality of working electrodes WE1-WE6 as well as reference and counter (auxiliary) electrodes RE, CE. More or fewer working electrodes may be used in other embodiments. In some embodiments of the invention, the reference and counter electrodes may be combined as a pseudo-reference electrode. An electrochemical cell is formed between the working and reference electrodes. To make measurements of a target solution that is in electrical connection with the electrodes, various voltages—static and time varying—are applied between ones of the working electrodes and the reference electrodes and the resulting currents detected. For example, ruthenium (Ru) concentration in a sample can be determined by applying a constant voltage and measuring current. - Overall control of the
electronics unit 10 of the sensor device is performed by amicro controller 101 which includes an internal memory to store system software. The micro controller may be a dedicated ASIC, an FPGA or a suitably programmed general purpose controller. The micro controller controls apotentiostat 104 via digital toanalog converter 103 and receives measurement results from the potentiostat 102 via analog to digital converter 102. Thepotentiostat 104 applies the desired voltages to the working, reference and counter electrodes WE, RE, CE; acell multiplexer 105 under the control ofmicroprocessor 101 selects the appropriate one of the working electrodes. The electrodes are preferably micro-electrodes, e.g. having a width of less than about 50 μm, microband electrodes or a micro-electrode array. - A
graphics display 108 enables display of operating menus to the user, options being input viakeypad 109, and measurement results. An electricallyerasable RAM 120 allows for storage of constants and measurement information. A bar code reader may also be provided for input of data, especially of patient information if the sensor is used in a medical or veterinarian application. Interfaces, e.g. conforming RS232, Bluetooth, Ethernet, USB, or WiFi (IEEE 802.11a, b, g, etc.) standards, may be provided for connection to printers, networks and other devices, e.g. patients records systems. The separately illustrated circuits may be combined onto one or more ASICs or FPGAs. - Power is supplied from
batteries 107 under the control of apower management unit 106 that optimises battery life and controls recharging of the batteries. - When a desired potential difference is to be applied to the electrochemical cell, if the output of the potentiostat is simply raised in a step function to that potential, a transient current will occur. The size of the initial current peak and the rate of decay will depend on factors such as the applied potential, as well as the capacitance, inductance and resistance of the electrochemical cell and the conductors leading to it. The capacitance and resistance of the electrochemical cell will be determined in part by the concentration of ions in the sample to be measured and hence the shape of the transient current cannot be predicted with sufficient accuracy. Current saturation in the amplifier of the potentiostat adds further complication. If current measurements are taken before the transient current has fully decayed, errors will result. In a portable device it is difficult to provide a large current sink to absorb the transient current rapidly so that a significant delay must be observed before measurements are taken. This increases measurement times which is particularly undesirable if multiple measurements are to be taken of a given sample.
- To avoid the generation of substantial transient currents, the present embodiment applies a potential waveform as shown in
FIG. 2 to the electrochemical cell. The waveform may be generated by providing a series of digital values as inputs to the digital toanalog converter 103 which then drives thepotentiostat 104. Suitable digital values can be calculated by a simple algorithm executed by themicrocontroller 101 or calculated in advance and stored in memory. - The waveform applied to the electrochemical cell has two parts, in the first (t0 to t4) a positive potential is applied to the cell and in the second (t4 to t8) a negative potential is applied. In this example the second part has a similar structure to the first part but opposite polarity and a different magnitude. However, the second part may instead have the same polarity and magnitude and may also be omitted if not required—e.g. to provide additional measurements.
- In both parts of the waveform, after an initial delay, t0 to t1, at which the voltage is held at substantially 0 the waveform ramps up to a desired voltage +V1 in the period t1 to t2. The voltage in this period conforms to a part of a sinusoidal curve—approximately half a cycle—to minimise the transient current, however other waveforms may be applied. After the ramp-up portion there is a plateau, t2 to t4, during which the potential applied to the cell is held substantially constant. The current through the cell is sampled during the latter part of the plateau, between times t3 and t4. The number of samples and the data rate may be chosen to suit the specific electrochemical measurement being made but for example 20 samples may be taken at a rate of about 300 Hz. The potential difference applied to the electrochemical cell during measurements, i.e. the plateau potential, will depend on the species to be detected an/or measured. Potentials in the range of ±2V (measured against an Ag/AgCl electrode) are suitable.
- As mentioned above, the negative-going part of the example waveform has ramp-up and plateau portions t5 to t6 and t6 to t8 that are inversions of the corresponding portions of the positive-going part of the example waveform. Of course in other embodiments, the second part of the waveform may have the same polarity as the first part and/or a different magnitude.
- During the ramp-up portion, the maximum slope is determined to keep the transient current below levels that can be sunk in the amplifier of the potentiostat. For example, a rate of about 50Vs−1 is suitable. This would provide a rise from 0 to ±0.5V in about 100 ms. A step potential, in which the potential is raised in less than 1 ms could result in a rate of 600Vs−1.
- At the end of the plateau, the voltage can be returned to zero as rapidly as desired if transients will not effect any further measurements but a soft ramp down may also be used, especially if other measurements are to be performed soon after.
- As the aim of the ramp-up portion is to prevent overload of the IE converter that forms part of the potentiostat, the required rate of potential change can be determined from consideration of a basic potentiostat circuit, such as that shown in
FIG. 3 . The modulation input to the potentiostat is shown at the right hand side of the figure and is amplified and applied to the common electrode CE of the electrochemical cell. The electrometer buffers the electrochemical potential of the reference electrode RE and feeds this potential back into a summing amplifier such that the potential of the counter electrode is maintained relative to the reference electrode. The IE converter converts the current i flowing out of the working electrode to a voltage output V=RB*i, where RB is the value of the feedback resister of the IE converter, which is essentially an operational amplifier current follower circuit. - In a practical circuit the maximum voltage output of the operational amplifier is limited by the power supply voltage and the characteristics of the operational amplifier selected. It is implicit that the voltage output of an operational amplifier cannot exceed its power supply voltage.
- Given that the voltage output of the IE converter is given by V=RB*i. There will be a maximum value of i, which can be input to the circuit, which is defined by the power supply voltage. In the situation where i exceeds this value the voltage output of the operational amplifier is limited by the power supply voltage. This output is no longer representative of the current i. The effect on the negative input should also be considered. In normal operation the potential at the negative input is zero, being the sum of i and the current through RB. In the overload condition the current though RB is no longer sufficient to match i, the result of this is that the potential at the negative input is no longer held at zero, but rises towards the potential at CE in three electrode systems, or shifts with the pseudo-reference electrode in two electrode systems. This causes the potentiostat to lose potential control and thus the electrochemical cell is no longer held at the desired potential. It follows that the current though the electrochemical cell is then limited by the saturation of the IE converter. Thus, the maximum ramp-up rate should be set to prevent saturation of the IE converter, which effectively means that the transient current should not be greater than the maximum current to be measured.
- This condition is particularly true in battery powered instruments where the power supply voltages are required to be a minimum to conserve power and reduce the circuitry.
- Whilst the invention has been described above in relation to a specific embodiment, the present invention may be embodied in other forms. For example, other functions may be used to define the ramp-up, including a linear sweep, logarithmic functions, sigmoidal functions, hyperbolas, logistic functions, Weibull functions, Gompertz growth model, Hill function, Chapman model. Polarities in this document are defined using IUPAC conventions but the results can readily be converted to other conventions. The scope of the invention is therefore determined by the appended claims rather than the foregoing description.
Claims (23)
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB0418346.3 | 2004-08-17 | ||
GB0418345A GB2417323A (en) | 2004-08-17 | 2004-08-17 | A method of operating an electrochemical sensor by applying a time variable potential between the electrodes. |
PCT/GB2005/003054 WO2006030170A1 (en) | 2004-08-17 | 2005-08-03 | Electrochemical sensor |
Publications (2)
Publication Number | Publication Date |
---|---|
US20070285099A1 true US20070285099A1 (en) | 2007-12-13 |
US7545148B2 US7545148B2 (en) | 2009-06-09 |
Family
ID=33042199
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US11/660,255 Active 2026-03-30 US7545148B2 (en) | 2004-08-17 | 2005-08-03 | Electrochemical sensor |
Country Status (12)
Country | Link |
---|---|
US (1) | US7545148B2 (en) |
EP (1) | EP1782054B1 (en) |
JP (1) | JP4819052B2 (en) |
CN (1) | CN101002086B (en) |
AT (1) | ATE472727T1 (en) |
CA (1) | CA2577477C (en) |
DE (1) | DE602005022080D1 (en) |
ES (1) | ES2345938T3 (en) |
GB (1) | GB2417323A (en) |
MX (1) | MX2007001883A (en) |
PL (1) | PL1782054T3 (en) |
WO (1) | WO2006030170A1 (en) |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20070285238A1 (en) * | 2006-06-12 | 2007-12-13 | Intelleflex Corporation | Rfid sensor tag with manual modes and functions |
US20110089957A1 (en) * | 2009-10-16 | 2011-04-21 | Microchips, Inc. | Multi-channel potentiostat for biosensor arrays |
WO2023026117A1 (en) * | 2021-08-23 | 2023-03-02 | King Abdullah University Of Science And Technology | Small-sized, reconfigurable, multi-measurement potentiostat circuitry and method |
Families Citing this family (12)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB0711780D0 (en) | 2007-06-18 | 2007-07-25 | Oxford Biosensors Ltd | Electrochemical data rejection methodology |
GB0715036D0 (en) * | 2007-08-02 | 2007-09-12 | Oxford Biosensors Ltd | Shoulder elimination |
GB0814238D0 (en) * | 2008-08-04 | 2008-09-10 | Oxford Biosensors Ltd | Enhancement of electrochemical response |
EP2656060B1 (en) | 2010-12-20 | 2021-03-10 | Roche Diabetes Care GmbH | Controlled slew rate transition for electrochemical analysis |
KR101333410B1 (en) * | 2011-11-01 | 2013-11-28 | 명지대학교 산학협력단 | Multiple potentiostat circuit and detection system using the same |
GR1008045B (en) * | 2012-05-22 | 2013-11-25 | ΜΙΚΡΟ-ΣΥΣΤΗΜΑΤΑ ΜΙΚΡΟ-ΡΟΗΣ ΓΙΑ ΓΕΝΕΤΙΚΟΥΣ ΕΛΕΓΧΟΥΣ ΚΑΙ ΜΟΡΙΑΚΗ ΔΙΑΓΝΩΣΤΙΚΗ ΕΠΕ με δ.τ. "Micro2Gen", | Parameterisable calibrated circuit for parallel measurements of an array of electrochemical sensors under continuous polarosation in real time |
WO2014140172A1 (en) | 2013-03-15 | 2014-09-18 | Roche Diagnostics Gmbh | Methods of failsafing electrochemical measurements of an analyte as well as devices, apparatuses and systems incorporating the same |
EP3388823A1 (en) | 2013-03-15 | 2018-10-17 | Roche Diabetes Care GmbH | Methods of scaling data used to construct biosensor algorithms as well as devices, apparatuses and systems incorporating the same |
JP6356707B2 (en) | 2013-03-15 | 2018-07-11 | エフ.ホフマン−ラ ロシュ アーゲーF. Hoffmann−La Roche Aktiengesellschaft | Method for detecting high antioxidant levels during electrochemical measurements and then fail-safe analyte concentration and devices, apparatus and systems incorporating the same |
JP6352954B2 (en) | 2013-03-15 | 2018-07-04 | エフ.ホフマン−ラ ロシュ アーゲーF. Hoffmann−La Roche Aktiengesellschaft | Method and device for using information from recovery pulses in electrochemical analyte measurement, apparatus and system incorporating them |
CA3123430A1 (en) | 2014-11-03 | 2016-05-12 | F. Hoffmann-La Roche Ag | Electrode arrangements for electrochemical test elements and methods of use thereof |
KR102372113B1 (en) | 2016-10-05 | 2022-03-07 | 에프. 호프만-라 로슈 아게 | Detection reagents and electrode arrangements for multi-analyte diagnostic test elements, and methods of using the same |
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SU399775A1 (en) * | 1971-07-21 | 1973-10-03 | И. Е. Брыксин, Р. М. Ф. Салихджанова , И. Белицкий Всесоюзный научно исследовательский институт автоматизации черной металлургии | VARIABLE WAY OF POLAROGRAPHIC ANALYSIS |
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2004
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-
2005
- 2005-08-03 MX MX2007001883A patent/MX2007001883A/en active IP Right Grant
- 2005-08-03 ES ES05768051T patent/ES2345938T3/en active Active
- 2005-08-03 CA CA2577477A patent/CA2577477C/en active Active
- 2005-08-03 JP JP2007526558A patent/JP4819052B2/en active Active
- 2005-08-03 DE DE602005022080T patent/DE602005022080D1/en active Active
- 2005-08-03 CN CN2005800273578A patent/CN101002086B/en active Active
- 2005-08-03 US US11/660,255 patent/US7545148B2/en active Active
- 2005-08-03 PL PL05768051T patent/PL1782054T3/en unknown
- 2005-08-03 AT AT05768051T patent/ATE472727T1/en active
- 2005-08-03 EP EP05768051A patent/EP1782054B1/en active Active
- 2005-08-03 WO PCT/GB2005/003054 patent/WO2006030170A1/en active Application Filing
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US4897162A (en) * | 1986-11-14 | 1990-01-30 | The Cleveland Clinic Foundation | Pulse voltammetry |
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US6558529B1 (en) * | 2000-02-07 | 2003-05-06 | Steris Inc. | Electrochemical sensor for the specific detection of peroxyacetic acid in aqueous solutions using pulse amperometric methods |
US20060191788A1 (en) * | 2001-11-26 | 2006-08-31 | Ischemia Technologies, Inc. | Electrochemical detection of ischemia |
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Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20070285238A1 (en) * | 2006-06-12 | 2007-12-13 | Intelleflex Corporation | Rfid sensor tag with manual modes and functions |
US7796038B2 (en) * | 2006-06-12 | 2010-09-14 | Intelleflex Corporation | RFID sensor tag with manual modes and functions |
US20110089957A1 (en) * | 2009-10-16 | 2011-04-21 | Microchips, Inc. | Multi-channel potentiostat for biosensor arrays |
US8604810B2 (en) * | 2009-10-16 | 2013-12-10 | Microchips, Inc. | Multi-channel potentiostat for biosensor arrays |
WO2023026117A1 (en) * | 2021-08-23 | 2023-03-02 | King Abdullah University Of Science And Technology | Small-sized, reconfigurable, multi-measurement potentiostat circuitry and method |
Also Published As
Publication number | Publication date |
---|---|
EP1782054A1 (en) | 2007-05-09 |
PL1782054T3 (en) | 2011-12-30 |
EP1782054B1 (en) | 2010-06-30 |
CA2577477A1 (en) | 2006-03-23 |
CA2577477C (en) | 2012-12-04 |
ATE472727T1 (en) | 2010-07-15 |
MX2007001883A (en) | 2007-04-24 |
CN101002086A (en) | 2007-07-18 |
CN101002086B (en) | 2010-11-10 |
ES2345938T3 (en) | 2010-10-06 |
JP4819052B2 (en) | 2011-11-16 |
WO2006030170A1 (en) | 2006-03-23 |
JP2008510157A (en) | 2008-04-03 |
US7545148B2 (en) | 2009-06-09 |
GB0418345D0 (en) | 2004-09-22 |
DE602005022080D1 (en) | 2010-08-12 |
GB2417323A (en) | 2006-02-22 |
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